Molecular chaperone proteins also referred to as heat shock proteins, are ubiquitous highly conserved proteins that bind to unstable proteins and aid in their refolding to maintain proper and stable conformation (Macario and Conway 2002; Ohtsuka and Suzuki 2000; Sherman and Goldberg 2001; Soti and Csermely 2002b; Soti and Csermely 2002a). Furthermore, molecular chaperone proteins have additional functions such as: 1) shuttling proteins to the nucleus; 2) acting as a transcriptional factor in cell regulation; 3) and providing weak binding abilities to normal proteins within the cell in order to maintain elements of cellular networks (Sherman and Goldberg 2001; Soti and Csermely 2002b; Soti and Csermely 2002a). Environmental and oxidative stresses lead to the expression of molecular chaperone proteins, which bind to the hydrophobic surfaces of damaged and denatured proteins, allowing for their proper folding and prevention of precipitation and aggregation of these proteins, ultimately preventing cell death (Macario and Conway 2002).
As the organism ages, cells are prone to mutations, posttranslational aberrations, increased oxidative and environmental stresses, resulting in greater aggregation of proteins (Giffard et al. 2004; Muchowski and Wacker 2005). Ageing of the organism may also lead to deficiencies in the anti-stress mechanism such as decreased molecular chaperone synthesis and inefficiencies in the ubiquitin-proteosome and lysosome-mediated autophagy degradation pathways (Muchowski and Wacker 2005). Recent reports have implicated deficiencies in molecular chaperone recruitment to the progression of many neurodegenerative and neurodevelopmental diseases such as: Parkinsons, Alzheimers and schizophrenia (Ohtsuka and Suzuki 2000; Sherman and Goldberg 2001; Soti and Csermely 2002a). This concept is especially important in post-mitotic cells such as neurons, which leads to massive accumulation of aggregated proteins (Soti and Csermely 2002a).
The presence of a unique class of brain-specific proteins, which bind to DA and structurally related catecholamines has recently been reported. These proteins have been termed catecholamine-regulated proteins (CRPs) (Ross et al. 1993; Ross et al. 1995). Three species of CRP (with molecular weights of 26, 40, and 47-kDa, respectively) have been isolated. Pharmacological and biochemical studies have shown no similarity between these particular proteins, known catecholamine binding proteins or receptors present in the brain (Modi et al. 1996; Ross et al. 1993; Ross et al. 1995). However, these particular proteins have high homology with the heat shock protein family. For example, molecular cloning of bovine brain CRP40 (Genbank #AF047009) revealed that this protein is related to the heat shock protein 70 kDa (Hsp70) family. As discussed earlier, heat shock proteins act as molecular chaperones and protect the cell from oxidative and other types of stresses (Ben Zvi and Goloubinoff 2001; Grover 2002; Soti and Csermely 2002b; Soti and Csermely 2002a).
Mortalin is a mitochondrial heat shock protein that was discovered in 1991 as a 66kDa protein in mouse embryonic fibroblasts (Wadhwa et al. 1991). In order to trace molecular mechanisms of cell immortalization, studies using mouse embryonic fibroblasts identified mortalin as a mortality marker. The protein was cloned and characterized as Mortalin-1 (mot-1) in the cytoplasm of murine fibroblast cells (Wadhwa et al. 1991). Transfected mot-1 cDNA in NIH3T3 cells was distributed in the cytoplasm and resulted in cell senescence. In contrast, the mot-2 cDNA isoform was encoded in the perinuclear region and resulted in the malignant transformation of NIH 3T3 cells ultimately inducing cell immortalization in normal human fibroblasts (Kaul et al. 2003). Interestingly, the mot-1 and mot-2 proteins differ from each other by only 2 amino acid residues and the 2 murine mortalin isoforms come from two separate genes (Xie et al. 2000).
The mot-2 protein has been described as a multifunctional protein due to its diverse functions (chaperone, anchoring protein and signal transduction). Recent reports have shown that the N-terminus of the mot-2 protein binds to the carboxyl end of the tumor suppressor gene p53 (Kaul et al. 2002; Wadhwa et al. 2002). This binding property inhibits the transactivation of p53 to the nucleus, resulting in cell immortalization. Mot-2 has been recognized as an important biological marker in cancer tumor research.
The human genome project has discovered approximately 32000 genes in the human species (Human Genome Sequencing Consortium, Nature, 2000). With the use of high-throughput techniques of sequencing the human genome and Established Sequence Tags (EST's), the complexity of the human genome has increased dramatically (Graveley 2001; Modrek and Lee 2003; Wadhwa et al. 2002). EST's are derived from fully processed mRNA, which occur following the introduction of the 5′ capping, splicing, and polyadenylation of the 3′ end (Modrek and Lee 2003; Wadhwa et al. 2002). Alternate splicing involves the exon skipping of particular exons within a gene, which results in the generation of multiple transcripts encoding different proteins, with possibly different functions in 70-88% of the studies reported (Graveley 2001; Wadhwa et al. 2002). Alternate splicing occurs in the human genome with a frequency between 35-59%, which results in at least one splice alternative for each gene reported (Modrek and Lee 2003; Wadhwa et al. 2002).
With the aid of information gathered from the human genome project, it would be desirable to identify biomarkers effective to diagnose disease, such as neurological disease including neurodegenerative and neurodevelopmental disease, particularly since access to neuronal tissue to obtain this information is not possible.